Directional coupler switch wherein stripline ground conductor is moved relative to stripline coupling conductors

ABSTRACT

A directional coupler electric switch is provided having a housing circuit half and a housing cap half. A circuit card located within the housing circuit half has a stripline directional coupler circuit on the outer side and a grounding surface on the inner side. A second circuit card located within the housing cap half has a grounding circuit on the inner side. Connecting means are provided for the circuits within the housing at an edge thereof. The housing circuit half and the housing cap half are engaged so that the stripline directional coupler circuit is between the first and second circuit cards. The circuit card in the housing cap half is adapted to move relative to the other circuit card in the other housing half such that the grounding circuit can be moved into and out of coupling relationship with the stripline directional coupler circuit.

United States Patent 1 [111 3,747,927

Bolt et al. July 17, 1973 DIRECTIONAL COUPLER SWITCH WHEREIN STRIPLINE GROUND Primary Examiner-Paul L. Gensler CONDUCTOR 1s MOVED RELATIVE TO Attorney-Harold H. Sweeney, Jr. et a1. STRIPLINE COUPLING CONDUCTORS [75] Inventors: Murray H. Bolt, Raleigh, NC; ABSTRACT Edward llberbacher, A directional coupler electric switch is provided having 7 poughkeePsle, a housing circuit half and a housing cap half. A circuit 73 Assignee; International Business Machines card located within the housing circuit half has a strip- C ti Armonk, line directional coupler circuit on the outer side and a grounding surface on the inner side. A second circuit [22] filed: July 1972 card located within the housing cap half has a ground- 2 APPL 2 9 55 ing circuit on the inner side. Connecting means are provided for the circuits within the housing at an edge thereof. The housing circuit half and the housing cap [52] US. Cl. 333/7, 333/10 half are engaged so that the stripline directional cow [51] Int. Cl. HOlp 1/10, HOlp 5/14 l circuit is between h fi and Second Circuit [58] Field Of Search 333/10, 7 cards The circuit card i the housing cap half is adapted to move relative to the other circuit card in the [56] References Cited other housing half such that the grounding circuit can UNITED STATES T S be moved into and out of coupling relationship with the 3,221,275 11/1965 Wambsganss 333/10 stripline directional coupler circuit,

3,332,039 7/1967 Oh 3,560,885 2/1971 Chao 333 I0 333;) 9 Claims, 6 Drawing Figures Pmmmmfl 3.747. 021

sum 1 or 2 FIGJ PRIOR ART DIRECTIONAL COUPLER SWITCH WHEREIN STRIPLINE GROUND CONDUCTOR IS MOVED RELATIVE TO STRIPLINE COUPLING CONDUCTORS This invention relates to an electric switch, and more particularly to an electric switch formed of a directional coupler adapted for use in a keyboard.

Switching devices of the type requiring a contact closure to complete a circuit have been found to be unreliable and of too short a life for use in situations where a large number of makes and breaks of the contact are required such as in keyboard operation. Not only the contacts themselves tend to wear but they must be protected from interference from a dirty environment.

An object of the present invention is to provide a switch made from a directional coupler which requires no physical switch contacts.

It is another object of the present invention to provide a stripline directional coupler switch which is not affected by a dirty environment.

It is a further object of the present invention to provide a stripline directional coupler switch which can be made sufficiently small to be used in a keyboard application.

It is a further object of the present invention to provide a stripline directional coupler switch which is operable by a key such as found in a keyboard.

Briefly, a directional coupler electric switch is provided having a housing circuit half and a housing cap half. A circuit card located within the housing circuit half has a stripline directional coupler circuit on the outer side and a grounding surface on the inner side. Connectors for the directional coupler circuit and the grounding surface are located at an edge of the housing circuit half. A second circuit card located within the housing cap half has a ground circuit on the inner side thereof. Further connecting means for the grounding circuit are found at an edge of the housing cap half. The housing circuit half and the housing cap half are engaged so that the stripline directional coupler circuit is between the first and second circuit cards. One of the grounding circuits is adapted for movement relative to the directional coupler circuit so that the grounding circuit is moved into and out of coupling relationship with the stripline directional coupler circuit.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

FIG. I is a schematic diagram of the prior art threeelement directional coupler showing the input and output wave forms thereof.

FIG. 2 is a schematic diagram showing the housing circuit half with the circuit card located therein.

FIG. 3 is a schematic diagram showing the housing cap half of the switch with the circuit card having the grounding circuits thereon located in a recessed area.

FIG. 4 is a schematic diagram showing a side view of the housing circuit half and the housing cap half in engagement.

FIG. 5 is an isometric view showing the switch housing with the operating button stem and spring in place.

FIG. 6 is a schematic diagram showing the electrical connections for utilizing the stripline directional coupler switch in a keyboard.

Referring to FIG. I, there is shown a schematic diagram of the prior art three-element directional coupler as disclosed in U. S. Pat. No. 3,601,716, filed Dec. 24, I969. The middle conductive segment 28 is the main line conductive segment of the directional coupler. The coupling segment 30, has a terminal 32 at the righthand or B end. A further coupling segment 34 extends parallel to and spaced from the other side of the main line segment 28. The spacing of the further coupling segment 34 from the main line segment 28 is the same as the spacing S between the input coupling line segment 30 and the main line segment 28. This further coupling segment 34 is of the same width as the input coupling segment 30. The input coupling segment 30 and the further coupling segment 34 each have an opposite end thereof connected together by a stub connector 36. Tuus, the input coupling segment 30 has the left end A connected to the right end B of the further coupling segment 34. The left end A of the further coupling segment 34 is terminated in a terminating resistance 38 of a value equivalent to the characteristic impedance of the line to which the segment is connected. As shown, one end of terminating resistor 38 is connected to ground by a ground connection 40. The A end of the main transmission line 28 is likewise terminated in an impedance 42 having the samecharacteristic impedance as the line.

The directional coupler conductive segments are stripline-type conductors which are well known in the art.

These conductors are usually closely packed and can best be manufactured by utilizing one of the well known masking and etching techniques used extensively in the manufacture of printed circuits. It is necessary to have appropriate ground planes for operation of the directional coupler. These usually consist of thin sheets of copper 46 arranged both below and above the conductors. The segments 28, 30 and 34 are located on the polyglass base 44 which serves as a dielectric to electrically isolate the segments from the belowlocated ground plane 46. If the schematic arrangement shown in FIG. 1 has 8 mil wide segments W separated from one another by 6 mil spacings S and the segment length L is approximately 2 nanoseconds in electrical length or approximately 11 inches in polyglass, and the epoxy glass stripline package is approximately '14; inches thick, and l to 4 coupling ratio results. With a l to 4 coupling ratio, an input pulse of 1 volt amplitude applied at the input terminal 32 of the input coupling segment 30 provides an output pulse on the main line conductor 28 as indicated in FIG. 1.

The present invention consists of a means for selec tively removing one of the ground planes of the circuit. With the ground plane in place forward coupling is high and reverse coupling is low due to similar coupling coefficients for the inductive and capacitive components. When the ground plane is removed, an unbalance of the micro circuit configuration takes place. As a result, the directivity of the coupler will decrease. Thus, a receiver in the reverse leg of the coupler will have a higher voltage applied to its input. It has been found that a voltage variation of 4 to 1 can be achieved between the two states, that is, with the ground plane in place and out of place.

The removal of the ground plane or switching action is accomplished by arranging one of the ground planes in a special configuration within a push button type switching arrangement which is small and compact and is easily adapted for operation in a keyboard. The housing containing the directional coupler switch consists of I a housing circuit half and a housing cap half 12. The

housing circuit half 10 comprises a recessed area into which is fit a circuit card 14 having a directional coupler 16 formed thereon. The circuit card 14 is. made of a dielectric material and has on the back surface thereof, that is, the surface facing into the recessed area, a ground plane 18. On the front surface of the circuit card 14, that is, the surface facing out of the housing 10, there is arranged a directional coupler circuit 16. Thls circuit is formed of three striplines 20,22,24. The coupler is known as a tri-coupler and is the equivalent of the directional coupler set forth in U. S. Pat. N 0. 3,601 ,716, filed Dec. 24, 1969 and assigned to the same assignee as the present invention. As can be seen from FIG. 2, the stripline of the directional coupler consists of three conducting elements 20,22,24 which are arranged on the circuit card 14 in serpentine fashion. The electrical connections to the circuit are made at the Input pins shown at the bottom of the housing 10. The first pin 26 is the shield pin which connects the ground plane shield 18 to the outside from the circuit card 14. The second pin 28 is the input pin to which the driver circuit would be connected. The input coupling segment of the stripline coupler is connected to the other end of pin 28. The third pin 29 connects the middle conductor segment or coupling segment 22 of the directional coupler 16 to the receiver for that particular directional coupler. It will be appreciated, that the stripline conductors 20,22,24 return in a serpentine fashion and the outputs therefrom are connected to output pins 50,52. As can be seen, the coupling segment 24 connects to pin 50 which can be connected to the next directional coupler on another switch. Pin 52 is the output pin of the directional coupler 16 and has the receiver connected thereto for receiving a pulse output from the stripline directional conductor when the switch is operated. It will be appreciated that the output end of stripline conducting segment is connected directly to the input end of the stripline segment 24 as Is the case in the tri-coupler previously discussed. This is the same connection referred to as the stub connector 36 in FIG. 1. The housing circuit half 10 has lock studs 54 extending from the four corners thereof which fit into corresponding openings 56 in the housing cap half 12 to correctly engage the'two halves into a single housing 58 as shown in FIG. 4.

The housing cap half 12 contains a further circuit card 60 made of a dielectric material and having a wide copper ground circuit 62 etched on the backside thereof. This is the card surface that faces into the recessed area 64 in the housing cap half 12 which holds the card 60. It should be noted that the copper ground plane circuit 62 has a serpentine arrangement similar to the directional coupler circuit so that when the two housing halves are secured together the copper ground plane circuit 62 has the same serpentine path and is contiguous with the directional coupler circuit 16 thereby forming a ground plane circuit of the directional coupler. The recessed area 64 in the housing cap half 12 is longer than the grounding circuit card 60. The recessed area 64 also has guide elements 66 therein along the sides so that the card 60 can be moved up and down within the recessed area 64. The card 60 is attached to a push button stem 68 which protrudes from the upper wall of the housing cap half 12.

Referring to FIG. 4, the housing halves 10,12 are shown secured together by means of the locking studs 54 and corresponding openings 56. The cards 14 and 60 are shown in their initial state. That is, with the directional coupler circuit 16 symmetrical so that it operates in a normal mode. This mode is with the ground circuit 62 contiguous with the directional coupler circuit lines. Pressing the push button stem 68 down moves the ground circuit card 60 relative to the tricoupler circuit card 14 so that the ground circuit 62 is moved into the area between the loops of the serpentine path of the directional coupler circuit 16. A return spring 70 is engaged by the push button stem 68 so that the stem is returned to its initial position after being pushed. The initial condition of the tri-coupler circuit 16 is in its symmetrical form, that is, with the ground plane circuit 62 in operational position so the switch operates normally. Pushing the button removes the ground plane circuit 62 so that the directional coupler circuit 16 is no longer symmetrical and thus the normal operation is interrupted.

FIG. 5 is an isometric view of the directional coupler switch showing the mounting of the spring 70 with respect to the stem 68 and schematically showing a key 72 attached to the stem 68 for operation, for example, as a keyboard element. The unit is adapted by means of the pins extending from the bottom of the housing for plug-in operation.

FIG. 6 is a schematic representation of the circuitry of the directional coupler connected in series as it would be used in a keyboard. The driver pulses are generated in driver 74 and travel in the lefthand direction along the coupling element 76. The directional coupler being a highly directive or directional unit causes coupling to the main conducting segment 78 inthe opposite direction. A resistor 80 having the required impedance to ground is utilized to terminate the pulse. When the ground plane is removed (not shown in FIG. 6) as described in connection with FIGS. 2, 3 and 4, the directivity of the directional coupler is essentially interferred with and the pulse couples in the forward direction (lefthand) along the main line segment 78 into the receiver 79. The driver pulse passes through the stub line 82 and travels in the same direction (leftliand) along the third conducting segment 84. This driver pulse passes to the next directional coupler 86 as the driver input via connector 88. Thus, the directional coupler circuits can be connected in' series and one driver circuit 74 is sufficient. As each button 72 in the keyboard is depressed, its receiver 79 receives a pulse indicating that the particular key has been pressed. The pulse ratio has been found to be 4 to 1 so that the directional coupler which is energized is readily identifiable.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A directional coupler electric switch comprising a housing circuit half and a housing cap half;

a circuit card located within said housing circuit half having a stripline directional coupler circuit on the outer side and a grounding surface on the inner side;

electrical connecting means for said directional coupler circuit and grounding surface;

a second circuit card located within said housing cap half and having a grounding circuit on the inner side;

electrical connecting means for said grounding circuit;

means for engaging said housing circuit half and said housing cap half so that the stripline directional coupler circuit is between said first and second circuit cards; and

means for moving one of said circuit cards relative to the other so that said grounding circuit can be moved into and out of coupling relationship with said stripline directional coupler circuit.

2. A directional coupler electric switch according to claim 1, wherein said stripline directional coupler circuit is arranged in a serpentine configuration on said circuit card, the distance between adjacent loops of said stripline directional coupler circuit in said serpentine configuration being at least as great as the width of said stripline directional coupler circuit.

3. A directional coupler electric switch according to claim 2, wherein said grounding circuit on said second circuit card has a serpentine configuration which is the mirror image of said stripline directional coupler circuit so that said grounding circuit and said stripline directional coupler circuit are contiguous when the housing circuit half and the housing cap half are engaged by said engaging means to form a complete housing.

4. A directional coupler electric switch according to claim 1, wherein said housing cap has a recessed area for receiving said second circuit card, said recessed area being longer than said second circuit card and having guide means along the edges thereof for guiding the second circuit card for movement within said recessed area.

5. A directional coupler electric switch according to claim 4, wherein said housing cap half has a further open portion at the top thereof connecting to said recessed area through the top of said housing cap half.

6. A directional coupler electric switch according to claim 5, wherein said means for moving one circuit card relative to the other includes a stern portion extending from the top of said second circuit card and extending through and beyond said further open portion at the top of said housing cap half so that said second circuit card can be moved relative to said first circuit card by depressing said stem portion.

7. A directional coupler according to claim 6, wherein the movement of said second circuit card relative to said first circuit card caused by said stem depression produces a movement of said ground plane circuit on said second circuit card out of contiguous relationship with said stripline directional coupler circuit on said first circuit card so as to decouple said circuit and cause a signal pulse in the forward direction in said stripline directional coupler circuit.

8. A directional coupler electric switch according to claim 6, wherein a cap such as a keyboard key is attached to said stem for selective operation of said switch.

9. A directional coupler electric switch according to claim 8, wherein a spring means is associated with said second circuit card and is connected to oppose the movement of said second circuit card caused by the depressing of said key, said spring returning said second circuit card to its starting position after any movement thereof. 

1. A directional coupler electric switch comprising a housing circuit half and a housing cap half; a circuit card located within said housing circuit half having a stripline directional coupler circuit on the outer side and a grounding surface on the inner side; electrical connecting means for said directional coupler circuit and grounding surface; a second circuit card located within said housing cap half and having a grounding circuit on the inner side; electrical connecting means for said grounding circuit; means for engaging said housing circuit half and said housing cap half so that the stripline directional coupler circuit is between said first and second circuit cards; and means for moving one of said circuit cards relative to the other so that said grounding circuit can be moved into and out of coupling relationship with said stripline directional coupler circuit.
 2. A directional coupler electric switch according to claim 1, wherein said stripline directional coupler circuit is arranged in a serpentine configuration on said circuit card, the distance between adjacent loops of said stripline directional coupler circuit in said serpentine configuration being at least as great as the width of said stripline directional coupler circuit.
 3. A directional coupler electric switch according to claim 2, wherein said grounding circuit on said second circuit card has a serpentine configuration which is the mirror image of said stripline directional coupler circuit so that said grounding circuit and said stripline directional coupler circuit are contiguous when the housing circuit half and the housing cap half are engaged by said engaging means to form a complete housing.
 4. A directional coupler electric switch according to claim 1, wherein said housing cap has a recessed area for receiving said second circuit card, said recessed area being longer than said second circuit card and having guide means along the edges thereof for guiding the second circuit card for movement within said recessed area.
 5. A directional coupler electric switch according to claim 4, wherein said housing cap half has a further open portion at the top thereof connecting to said recessed area through the top of said housing cap half.
 6. A directional coupler electric switch according to claim 5, wherein said means for moving one circuit card relative to the other includes a stem portion extending from the top of said second circuit card and extending through and beyond said further open portion at the top of said housing cap half so that said second circuit card can be moved relative to said first circuit card by depressing said stem portion.
 7. A directional coupler according to claim 6, wherein the movement of said second circuit card relative to said first circuit card caused by said stem depression produces a movement of said ground plane circuit on said second circuit card out of contiguous relationship with said stripline directional coupler circuit on said first circuit card so as to decouple said circuit and cause a signal pulse in the forward direction in said stripline directional coupler circuit.
 8. A directional coupler electric switch according to claim 6, wherein a cap such as a keyboard key is attached to said stem for selective operation of said switch.
 9. A directional coupler electric switch according to claim 8, wherein a spring means is associated with said second circuit card and is connected to oppose the movement of said second circuit card caused by the depressing of said key, said spring returning said second circuit card to its starting position after any movement thereof. 